<template>
	<div class="music-list">
		<div class="back" @click="back">
			<i class="icon-back"></i>
		</div>
		<h1 class="title" v-html="title"></h1>
		<div class="bg-image" :style="bgStyle" ref="bgImage">
			<div class="play-wrapper">
        <div ref="playBtn" v-show="songs.length" class="play" @click="random">
          <i class="icon-play"></i>
          <span class="text">随机播放全部</span>
        </div>
      </div>
			<div class="filter"></div>
		</div>
		<div class="bg-layer" ref="layer"></div>
			<scroll :data="songs"
			 @scroll="scroll"
       :listen-scroll="listenScroll" 
       :probe-type="probeType" 
       class="list" ref="list">
				<div class="song-list-wrapper">
					<song-list @select="selectItem" :songs="songs"></song-list>
				</div>
				<div v-show="!songs.length" class="loading-container">
	        <loading></loading>
	      </div>
			</scroll>
	</div>
</template>

<script>
import Scroll from 'base/scroll/scroll' 
import SongList from 'base/song-list/song-list'
import Loading from 'base/loading/loading'
import {prefixStyle} from 'common/js/dom'
import {mapActions} from 'vuex'

const RESERVED_HEIGHT = 40
const transform = prefixStyle('transform')
const backdrop = prefixStyle('backdrop-filter')

export default {
	components: {
		Scroll,
		Loading,
		SongList
	},
	props: {
    bgImage: {
      type: String,
      default: ''
    },
    songs: {
      type: Array,
      default: []
      //default: () => []  //props default 数组／对象的默认值应当由一个工厂函数返回
    },
    title: {
      type: String,
      default: ''
    }
  },
  data() {
    return {
      scrollY: 0
    }
  },
  computed: {
    bgStyle() {
      return `background-image:url(${this.bgImage})`
    }
  },
  created() {
    this.probeType = 3  //设置用来监听滚动距离
    this.listenScroll = true
  },
  mounted () {
  	this.imageHeight = this.$refs.bgImage.clientHeight
    this.minTransalteY = -this.imageHeight + RESERVED_HEIGHT
    this.$refs.list.$el.style.top = `${this.imageHeight}px`
  },
  methods: {
  	back() {
      this.$router.back()
    },
    scroll(pos) {
      this.scrollY = pos.y
    },
    selectItem(item, index) {
    	this.selectPlay({
    		list: this.songs,
    		index: index
    	})
    },
    random() {
  	  this.randomPlay({
        list: this.songs
      })
    },
    ...mapActions([
    		'selectPlay',
    		'randomPlay'
    	])
  },
  watch: {
  	scrollY(newY) {
  		let translateY = Math.max(this.minTransalteY, newY)
  		let zIndex = 0
  		let scale = 1
      let blur = 0
  		const percent = Math.abs(newY / this.imageHeight)  //绝对值
  		if (newY > 0) {
        scale = 1 + percent
        zIndex = 10
      } else {
        blur = Math.min(20, percent * 20)  //最大为20
      }

  		this.$refs.layer.style[transform] = `translate3d(0,${translateY}px,0)`
  		if(newY < this.minTransalteY) {
  			zIndex = 10
  			this.$refs.bgImage.style.paddingTop = 0
  			this.$refs.bgImage.style.height = `${RESERVED_HEIGHT}px`
  			this.$refs.playBtn.style.display = 'none'
  		} else {
  			this.$refs.bgImage.style.paddingTop = '70%'
  			this.$refs.bgImage.style.height = 0
  			this.$refs.playBtn.style.display = ''
  		}
  		this.$refs.bgImage.style.zIndex = zIndex
  		this.$refs.bgImage.style[transform] = `scale(${scale})`

  	}
  }
}
</script>

<style scoped lang="stylus">
	@import "~common/stylus/variable"
	@import "~common/stylus/mixin"
	
	.music-list
		position: fixed
		z-index: 100
		top: 0
		left: 0
		bottom: 0
		right: 0
		background: $color-background
		.back
			position: absolute
			top: 0
			left: 6px
			z-index: 50
			.icon-back
				display: block
				padding: 10px
				font-size: $font-size-large-x
				color: $color-theme
		.title
			position: absolute
			top: 0
			left: 10%
			z-index: 40
			width: 80%
			no-wrap()
			text-align: center
			line-height: 40px
			font-size: $font-size-large
			color: $color-text
		.bg-image
			position: relative
			width: 100%
			height: 0
			padding-top: 70%
			transform-origin: top
			background-size: cover
			.play-wrapper
				position: absolute
				bottom: 20px
				z-index: 50
				width: 100%
				.play
					box-sizing: border-box
					width: 135px
					padding: 7px 0
					margin: 0 auto
					text-align: center
					border: 1px solid $color-theme
					color: $color-theme
					border-radius: 100px
					font-size: 0
					.icon-play
						display: inline-block
						vertical-align: middle
						margin-right: 6px
						font-size: $font-size-medium-x
					.text
						display: inline-block
						vertical-align: middle
						font-size: $font-size-small
			.filter
				position: absolute
				top: 0
				left: 0
				width: 100%
				height: 100%
				background: rgba(7, 17, 27, 0.4)
		.bg-layer
			position: relative
			height: 100%
			background: $color-background
		.list
			position: fixed
			top: 0
			bottom: 0
			width: 100%
			background: $color-background
			.song-list-wrapper
				padding: 20px 30px
			.loading-container
				position: absolute
				width: 100%
				top: 50%
				transform: translateY(-50%)
</style>